Conveying driving device, conveying driving device control method, and storage medium storing control program for conveying driving device, motor drive current setting table generating method and storage medium storing program for generating motor drive current setting table, image forming apparatus, image forming apparatus control method, and storage medium storing program for image forming apparatus

ABSTRACT

A conveying driving device of the invention includes a first motor which transmits power to a drive shaft of a roller; a second motor which transmits power to the drive shaft along with the first motor at a torque smaller than that of the first motor; and a controller which sets each of drive current setting values of the first motor and the second motor so that a total value of a consumption current of the first motor and the second motor becomes minimal in a steady state in which the roller rotates at a constant setting speed.

CROSS-REFERENCE TO RELATED APPLICATION

Japanese patent application No. 2017-236310 filed on Dec. 8, 2017,including description, claims, drawings, and abstract the entiredisclosure is incorporated herein by reference in its entirety.

BACKGROUND 1. Technological Field

The present invention relates to a conveying driving device, conveyingdriving device control method, and a storage medium storing a controlprogram for the conveying driving device, motor drive current settingtable generating method and a storage medium storing a program forgenerating the motor drive current setting table, an image formingapparatus, image forming apparatus control method, and a storage mediumstoring a program for the image forming apparatus.

2. Description of the Related Art

In recent years, a printing speed of an image forming apparatus has beenincreased. Along with this increase in printing speed, it is required toincrease a rotation speed of a conveying roller conveying a sheet and tosuppress power consumption of the apparatus.

Relating to this issue, Unexamined Japanese Patent Publication No.2002-159196 discloses a technique of performing an operation of drivinga conveying roller in an acceleration state and a stop state by astepping motor and performing an operation of driving the same conveyingroller in a steady state in which conveying a sheet at a constant speedby a DC brushless motor feedback-controlled on the basis of a rotationspeed of the motor. According to this technique, it is possible toensure positional accuracy in the acceleration state and the stop stateand to realize high efficiency and a high-speed rotation accuratelycontrolled in speed in the steady state.

Unexamined Japanese Patent Publication Nos. 2006-039095, 2006-017988,and 2007-058082 disclose a technique of rotating a drive shaft by powerof two motors by supplementally transmitting power of the DC brushlessmotor to the drive shaft driven by the stepping motor. According to thistechnique, it is possible to accelerate a conveying roller in a shorttime by reducing a load torque of the stepping motor at the time ofactivation.

SUMMARY

However, in the technique disclosed in Unexamined Japanese PatentPublication No. 2002-159196, since the conveying roller is driven onlyby the DC brushless motor in the steady state, a problem arises in thatconsumption power cannot be suppressed by the optimization of theconsumption current of the stepping motor and the DC brushless motor. Inthe technique disclosed in Unexamined Japanese Patent Publication Nos.2006-039095, 2006-017988, and 2007-058082, a problem arises in that theconsumption power of two motors is not considered.

The present invention has been made to solve such problems. That is, anobject of the invention is to provide a conveying driving device,conveying driving device control method and program, motor drive currentsetting table generating method and program, an image forming apparatus,and image forming apparatus control method and program capable ofsuppressing a motor consumption current in the steady state at the timeof driving the same drive shaft at different torques by two motors.

To achieve at least one of the abovementioned objects, according to anaspect of the present invention, a conveying driving device reflectingone aspect of the present invention comprises a first motor whichtransmits power to a drive shaft of a roller, a second motor whichtransmits power to said drive shaft along with said first motor at atorque smaller than that of said first motor, and a controller whichsets each of drive current setting values of said first motor and saidsecond motor so that a total value of a consumption current of saidfirst motor and said second motor becomes minimal in a steady state inwhich said roller rotates at a constant setting speed.

The objects, features, and characteristics of this invention other thanthose set forth above will become apparent from the description givenherein below with reference to preferred embodiments illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

The advantages and features provided by one or more embodiments of theinvention will become more fully understood from the detaileddescription given hereinbelow and the appended drawings which are givenby way of illustration only, and thus are not intended as a definitionof the limits of the present invention.

FIG. 1 is a cross-sectional view illustrating a schematic configurationof an image forming apparatus;

FIG. 2 is a plan view illustrating a schematic configuration of aconveying driving device of a registration roller;

FIG. 3 is a block diagram illustrating a control system of the drivingdevice;

FIG. 4 is a diagram illustrating a motor driver and a drive currentmeasurement circuit which are provided in a stepping motor;

FIG. 5 is a graph showing dependence of a STM drive current, a DCBLdrive current, and a total value of a consumption current with respectto a STM set current;

FIG. 6 is a graph showing load condition dependence of a relationshipbetween a STM set current and the total value of the consumptioncurrent;

FIG. 7 is a graph showing a relationship between the STM set current andthe total value of the consumption current in a steady state calculatedon the basis of a predetermined relational expression;

FIG. 8 is a diagram illustrating an example of a table that the STM setcurrent and the DCBL drive current in which the total value of theconsumption current in a steady state becomes minimal are registered foreach load condition;

FIG. 9 is a diagram illustrating a specific example of a load conditionand a registered value in a table that the STM set current and the DCBLdrive current in which the total value of the consumption current in thesteady state becomes minimal are registered for each load condition;

FIG. 10 is a flowchart illustrating an operation of the image formingapparatus;

FIG. 11 is a diagram illustrating another example of a table that theSTM set current and the DCBL drive current in which the total value ofthe consumption current in the steady state becomes minimal areregistered for each load condition;

FIG. 12 is a timing chart showing torques of the stepping motor and a DCbrushless motor, the STM set current, and the DCBL drive current in anacceleration state and the steady state along with a conveying speed anda required torque; and

FIG. 13 is a flowchart illustrating the operation of the image formingapparatus.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, one or more embodiments of the present invention will bedescribed with reference to the drawings. However, the scope of theinvention is not limited to the disclosed embodiments.

Hereinafter, a conveying driving device, conveying driving devicecontrol method and program, motor drive current setting table generatingmethod and program, an image forming apparatus, and image formingapparatus control method and program according to an embodiment of thepresent invention will be described with reference to the drawings. Inthe drawings, the same reference numerals will be given to the samecomponents and a repetitive description thereof will be omitted.Further, the dimensional ratios of the drawings are exaggerated forconvenience of description and may differ from the actual ratio.

First Embodiment

FIG. 1 is a cross-sectional view illustrating a schematic configurationof the image forming apparatus. The image forming apparatus 100 includesa controller 110, an operation panel 120, an image reader 130, an imageformer 140, a fixer 150, a feeder 160, and a sheet conveyor 170.

The controller 110 includes a Central Processing Unit (CPU) and variousmemories and performs control for each component or various calculationprocesses in accordance with a program.

The operation panel 120 includes a touch panel, ten keys, a startbutton, and a stop button and is used to display various pieces ofinformation and to input various instructions.

The image reader 130 includes a light source such as a fluorescent lampand an imaging device such as a Charge Coupled Device (CCD) imagesensor. The image reader 130 applies light from a light source to adocument set at a predetermined reading position, photoelectricallyconverts the reflected light by the imaging device, and generates imagedata from the electrical signal thereof.

The image former 140 includes image forming units 141Y to 141Kcorresponding to respective colors of yellow (Y), magenta (M), cyan (C),and black (K). The toner images which are formed by the charging,exposing, and developing processes of the image forming units 141Y to141K are sequentially laminated on an intermediate transfer belt 142 andare transferred onto a sheet 500 by a secondary transfer roller 143.

The fixer 150 includes a heating roller 151 and a pressing roller 152and heats and presses the sheet 500 conveyed to a fixing nip formedbetween both rollers 151 and 152 to melt and fix the toner image on thesurface of the sheet 500.

The feeder 160 includes a plurality of feeding trays 161 and 162 andsends the sheet 500 accommodated in the feeding trays 161 and 162 one byone toward a downstream side in a conveying path.

The sheet conveyor 170 includes a plurality of conveying rollers forconveying the sheet 500 and conveys the sheet 500 among the image former140, the fixer 150, and the feeder 160. The plurality of conveyingrollers include a registration roller 171 for correcting a skew of thesheet 500 and a loop roller 172 for forming a predetermined amount ofloop in the sheet 500. The registration roller 171 is driven by aconveying driving device 200 (see FIG. 2) including two motors.

FIG. 2 is a plan view illustrating a schematic configuration of theconveying driving device of a registration roller and FIG. 3 is a blockdiagram illustrating a control system of the driving device.

As illustrated in FIG. 2, the conveying driving device 200 includes astepping motor 210 and a DC brushless motor 220. The stepping motor 210and the DC brushless motor 220 respectively constitute a first motor anda second motor.

The stepping motor 210 is connected to a drive shaft 171 a of theregistration roller 171 through a plurality of gears 230 and 240 so asto be able to transmit power thereto. Further, the DC brushless motor220 is connected to the drive shaft 171 a of the registration roller 171through a plurality of gears 250 and 260 so as to be able to transmitpower thereto. The torque of the stepping motor 210 is set to be largerthan the torque of the DC brushless motor 220. Accordingly, theconveying driving device 200 operated in a so-called twin driving manneris obtained such that the power transmitted to the drive shaft 171 a bythe stepping motor 210 is assisted by the power transmitted to the driveshaft 171 a by the DC brushless motor 220. Furthermore, two motorsconnected to the drive shaft 171 a are not limited as long as the motorshave a difference in torque. That is, for example, instead of thestepping motor 210, a DC brushless motor having a torque larger thanthat of the DC brushless motor 220 may be used.

As illustrated in FIG. 3, the controller 110 of the image formingapparatus 100 includes an overall control CPU 111 and a motor controlCPU 112 and controls the operations of the stepping motor 210 and the DCbrushless motor 220.

The controller 110 controls the rotation speed of the stepping motor 210by transmitting a clock signal (CLK) to the stepping motor 210 andsetting an operation frequency of the stepping motor 210. The controller110 controls the torque of the stepping motor 210 by transmitting acurrent setting signal Vs to the stepping motor 210 and setting a drivecurrent setting value Is of the stepping motor 210. As will be describedlater, the controller 110 receives a voltage V_(R) corresponding to adrive current measurement value applied to the stepping motor 210 fromthe stepping motor 210.

The controller 110 controls the torque and the rotation speed of the DCbrushless motor 220 by transmitting a PWM signal to the DC brushlessmotor 220. The torque of the DC brushless motor 220 is controlled by aduty ratio of the PWM signal and the rotation speed is controlled by afrequency of the PWM signal.

FIG. 4 is a diagram illustrating a motor driver and a drive currentmeasurement circuit provided in the stepping motor.

A motor driver 211 includes a setting current source 211S and inverters211 a to 211 x. The motor driver 211 is a circuit which rotates a rotor(not illustrated) of the stepping motor 210 by supplying a pulsed drivecurrent (hereinafter, referred to as a “STM drive current”) from theinverters 211 a to 211 x to a plurality of coils (not illustrated) ofthe stepping motor 210.

The setting current source 211S supplies a DC current (hereinafter,referred to as a “STM set current”) set as the drive current settingvalue Is to the inverters 211 a to 211 x. The STM set currentconstitutes the drive current setting value of the first motor.

The inverters 211 a to 211 x convert the STM set current into a pulseddrive current by a clock signal input thereto and output the pulseddrive current to a plurality of coils of the stepping motor 210.

The drive current measurement circuit 212 includes a current detectionresistor 212R and an amplification circuit 212A. The current detectionresistor 212R is connected between the inverters 211 a to 211 x and aground and convert the drive current into a voltage V_(R)′. Theamplification circuit 212A generates a voltage V_(R) corresponding tothe STM drive current by amplifying the converted voltage V_(R)′ andtransmits the voltage V_(R) to the controller 110.

An effective value of the STM drive current changes depending on theoperation frequency of the stepping motor 210. That is, when theoperation frequency of the stepping motor 210 becomes higher, theinfluence of the parasitic resistance and the parasitic capacitance onthe path through which the drive current flows becomes remarkable andthe rise time of the STM drive current becomes relatively long, so thatthe effective value of the STM drive current decreases. Accordingly, thetorque of the stepping motor 210 decreases as the operation frequencyincreases.

The controller 110 calculates the STM drive current as the effectivevalue on the basis of the received voltage V_(R). Accordingly, thecontroller 110 obtains a STM drive current measurement value.

The controller 110 calculates the drive current of the DC brushlessmotor 220 set in the PWM signal transmitted to the DC brushless motor220 as the effective value. Hereinafter, the drive current of the DCbrushless motor 220 will be referred to as a “DCBL drive current”. TheDCBL drive current set in the PWM signal constitutes the drive currentsetting value of the second motor. The DCBL drive current may bemeasured. The controller 110 calculates the total value of the STM drivecurrent and the DCBL drive current as the total value of the consumptioncurrent of the stepping motor 210 and the DC brushless motor 220.Hereinafter, the total value of the STM drive current and the DCBL drivecurrent will be referred to as a “total value of a consumption current”.

FIG. 5 is a graph showing dependence of the STM drive current, the DCBLdrive current, and the total value of the consumption current withrespect to the STM set current. The STM drive current and the DCBL drivecurrent are values in a steady state in which the registration roller171 rotates at a constant setting speed (hereinafter, simply referred toas a “steady state”). The STM drive current and the DCBL drive currentare set so that the total value of the torques of these motor becomesequal to or larger than the torque required for the steady state.

The STM drive current decreases as the STM set current decreases. TheDCBL drive current increases as the STM set current decreases. This isbecause the torque of the stepping motor 210 which decreases with adecrease in the STM set current is compensated by increasing the DCBLdrive current in order to ensure the torque required for the steadystate.

According to the graph, it is understood that the total value of aconsumption current becomes minimal when the STM set current is 1.6 Aand the DCBL drive current is 0.1 A. It is understood that the STM drivecurrent when the total value of the consumption current becomes minimalis 0.7 A.

The controller 110 sets the STM set current and the DCBL drive currentin the steady state so that the total torque which is the total value ofthe torques of the stepping motor 210 and the DC brushless motor 220becomes equal to or larger than the torque required in the steady stateand the total value of the consumption current becomes minimal. A “casein which the total value of the consumption current becomes minimal”also includes a case in which the sum of the STM drive current and theDCBL drive current becomes a minimum value or slightly larger than theminimum value. The STM drive current is set by setting the STM setcurrent. That is, the setting of the STM set current corresponds to thesetting of the STM drive current. The DCBL drive current is set by theduty ratio of the PWM signal.

The controller 110 sets the STM drive current and the DCBL drive currentin the steady state so that the total value of the consumption currentbecomes minimal on the basis of the load condition of the registrationroller 171. The load condition can be specified on the basis of a printjob. The load condition may be at least one of the sheet types of theconveyed sheet and the sheet conveying speed (linear speed). The sheettype includes concepts of, for example, stiffness, thickness, and basisweight. The load condition may include a nip pressure at a nip portionformed by one roller to which power is transmitted from the steppingmotor 210 and the DC brushless motor 220 through the drive shaf and theother roller of the registration roller 171. The load condition includesa temperature. This is because, for example, a roller shape changes dueto the temperature so that a load on the roller changes. The loadcondition may include the load on the roller caused by the pulling ofthe sheet 500 due to the conveying speed difference of the sheet 500 atthe upstream and downstream of the roller.

The controller 110 can calculate the STM set current and the DCBL drivecurrent in which the total value of the consumption current in thesteady state becomes minimal on the basis of a predetermined relationalexpression. The controller 110 sets the STM set current and the DCBLdrive current which are calculated as described above as the STM setcurrent and the DCBL drive current in the steady state.

FIG. 6 is a graph showing load condition dependence of a relationshipbetween the STM set current and the total value of the consumptioncurrent.

According to the graph, it is understood that the total value of theconsumption current increases as a load increases.

A relationship between the total value of the consumption current andthe STM set current for each load condition in the steady state can beexpressed by, for example, Relational Expression (1).

y=a(x+b+λ)² +c+λ′  (1)

Here, y is the total value of the consumption current [A], x is the STMset current [A], λ and λ′ indicate correction constants corresponding tothe load condition, and a to c indicate constants. a to c can beobtained by, for example, an experiment. λ and λ′ constitute a firstload parameter and are constants for correcting the relationship betweenthe STM set current and the total value of the consumption current foreach load condition. λ and λ′ are each determined and obtained by, forexample, an experiment.

As detailed examples of Expression (1), Expressions (2) to (4) below areshown. Expression (2) is an expression when the load is relativelysmall, Expression (3) is an expression when the load is intermediate,and Expression (4) is an expression when the load is relatively large.

y=2.7(x−0.7)²+0.9  (2)

y=2.7(x−1.4)²+1.5  (3)

y=2.7(x−2.0)²+2.3  (4)

By Expression (1), it is possible to calculate the STM set current inwhich the total value of the consumption current in the steady statebecomes minimal. The calculated STM set current is a setting value forsetting the STM drive current and constitutes a first setting value.

The DCBL drive current at the time of setting the STM set current inwhich the total value of the consumption current in the steady statebecomes minimal can be calculated from the relational expression showinga relationship between the STM set current and the DCBL drive current.As a specific example of the relational expression showing arelationship between the STM set current and the DCBL drive current,Expression (5) below is shown.

z=2.7(x′−0.925)²−0.015  (5)

Here, z is the DCBL drive current [A] and x′ is the STM set current [A]in which the total value of the consumption current in the steady statebecomes minimal. The constants in the expression is a correctionconstant for correcting the relationship between the STM set current andthe DCBL drive current for each load condition and constitutes a secondload parameter. The correction constant can be obtained by, for example,an experiment. When the DCBL drive current in Expression (5) becomes anegative value, the DCBL drive current is set to 0.

The DCBL drive current calculated by Expression (5) constitutes a secondsetting value.

FIG. 7 is a graph showing the relationship between the STM set currentand the total value of the consumption current in the steady statecalculated on the basis of a predetermined relational expression. Thepredetermined relational expression indicates Expressions (2) to (4)described above. FIG. 7 also shows plots of measurement values of therelationship between the STM set current and the total value of theconsumption current in the steady state.

According to FIG. 7, the relationship between the STM set current andthe total value of the consumption current in the steady statecalculated on the basis of the predetermined relational expression issimilar to the measurement value. Further, as indicated by an asterisklocation, a calculation value obtained by the predetermined relationalexpression of the STM set current in which the total value of theconsumption current in the steady state becomes minimal is similar tothe measurement value.

The controller 110 can previously generate and store a table that theSTM set current and the DCBL drive current in which the total value ofthe consumption current in the steady state becomes minimal areregistered for each load condition. The controller 110 can set the STMset current and the DCBL drive current as the STM set current and theDCBL drive current setting value in a steady state for each loadcondition by referring to the table.

FIG. 8 is a diagram illustrating an example of the table that the STMset current and the DCBL drive current in which the total value of theconsumption current in the steady state becomes minimal are registeredfor each load condition. The load condition is the sheet type and theconveying speed. Specifically, the load condition of the sheet type isthe stiffness of the sheet. FIG. 9 is a diagram illustrating specifiedexamples of the load condition and the registered value in the tablethat the STM set current and the DCBL drive current in which the totalvalue of the consumption current in the steady state becomes minimal areregistered for each load condition.

According to the table, the STM set current and the DCBL drive currentincrease as the conveying speed increases. Furthermore, the total valueof the consumption current decreases in a case in which the STM setcurrent increases as the conveying speed increases. Further, when thestiffness of the sheet increases, since the current required for drivingthe stepping motor 210 and the DC brushless motor 220 increases, the STMset current and the DCBL drive current increase.

FIG. 10 is a flowchart illustrating an operation of the image formingapparatus. The flowchart can be performed according to a program by thecontroller 110 of the image forming apparatus 100.

The controller 110 acquires the torque (hereinafter, referred to as the“required torque”) required for transmitting power to the drive shaft171 a of the registration roller 171 in the steady state (S101). Thecontroller 110 can acquire the required torque corresponding to the loadcondition specified on the basis of the print job by referring to thetable in which the required torque is registered for each loadcondition.

The controller 110 sets the STM set current sufficient for the requiredtorque (S102). That is, the controller 110 sets the STM set current forgenerating a torque having a margin with respect to the required torquein the stepping motor 210.

The controller 110 measures the total value of the consumption currentby measuring the STM drive current at the time of conveying the sheet inthe steady state and calculating the DCBL drive current (S103).

The controller 110 determines whether the total value of the consumptioncurrent is smaller than a previous measurement value (S104).

When the total value of the consumption current is smaller than theprevious measurement value (S104: YES), the controller 110 decreases theSTM set current to decrease the STM drive current and increase the DCBLdrive current (S105). The controller 110 repeats step S103 to step S105until the total value of the consumption current becomes equal to orlarger than the previous measurement value.

When the total value of the consumption current is not smaller than theprevious measurement value (S104: NO), the controller 110 generates thetable by registering the STM set current and the DCBL drive current setin the previous measurement (S106).

In this way, the table is generated by the processes of steps S101 toS106. Then, after the table is generated, the controller 110 sets theSTM set current and the DCBL drive current in the steady state on thebasis of the table (S107) and forms an image on the conveyed sheet(S108).

FIG. 11 is a diagram illustrating another example of the table that theSTM set current and the DCBL drive current in which the total value ofthe consumption current in the steady state becomes minimal areregistered for each load condition. The load condition is at least oneof the sheet type, the conveying speed, the nip pressure, thetemperature, and the load on the roller caused by the pulling of thesheet due to a conveying speed difference of the sheet 500 at theupstream and downstream of the roller. The load condition of the sheettype may be the stiffness of the sheet. In this example, the STM setcurrent and the DCBL drive current in which the total value of theconsumption current in the steady state becomes minimal are registeredby the combination of three load conditions. For this reason, the tableof the STM set current and the DCBL drive current under two loadconditions of the sheet type and either of the nip pressure, thetemperature, and the load on the roller caused by the pulling of thesheet due to the sheet conveying speed difference at the upstream anddownstream of the roller. Further, the table of the STM set current andthe DCBL drive current under the two load conditions is required foreach load conditions other than the two load conditions, for example,each conveying speed setting value.

According to the table, the load on the registration roller 171increases as the load due to any one of the load conditions increases.For this reason, the STM set current and the DCBL drive current requiredfor driving the stepping motor 210 and the DC brushless motor 220increase.

FIG. 12 is a timing chart showing the torques of the stepping motor andthe DC brushless motor, the STM set current, and the DCBL drive currentin an acceleration state and the steady state along with the conveyingspeed and the required torque.

In the acceleration state, the controller 110 increases the conveyingspeed to a speed in the steady state from 0 at the time of starting theconveying operation. The STM set current is set so that the requiredtorque is sufficiently obtained only by the torque of the stepping motor210 at the time of starting the conveying operation. That is, the DCBLdrive current is set to 0 at the time of starting the conveyingoperation and the DCBL drive current is linearly increased in accordancewith an increase in rotation speed of the stepping motor 210. When theDCBL drive current is linearly increased, the torque of the DC brushlessmotor 220 is linearly increased.

In the acceleration state, when the conveying speed increases as therotation speed of the stepping motor 210 increases, the torque of thestepping motor 210 decreases. This is because the rise time of thepulsed STM drive current relatively increases and the effective value ofthe STM drive current decreases when the operation frequency of thestepping motor 210 increases as described above. As a result, therequired torque in the acceleration state is not obtained only by thetorque of the stepping motor 210. However, when the torque of the DCbrushless motor 220 which increases linearly is supplementally added tothe torque of the stepping motor 210, the total torque of the steppingmotor 210 and the DC brushless motor is sufficient for the requiredtorque in the acceleration state. The required torque in theacceleration state can be calculated by a general expression on thebasis of the inertia moment of the registration roller 171, thecharacteristic of the stepping motor 210, the load torque on thestepping motor 210, and the rotation speed of the registration roller171. The required torque in the acceleration state is, for example 400mNm.

The controller 110 controls the conveying speed at a constant speed inthe steady state. The conveying speed in the steady state is, forexample, 1129 mm/s.

Since the required torque in the steady state does not need the torquefor an acceleration, the required torque decreases as compared with theacceleration state. The required torque in the steady state is, forexample, 255 mNm. The controller 110 sets the STM set current and theDCBL drive current in the steady state so that the total torque of thestepping motor 210 and the DC brushless motor 220 is equal to or largerthan the required torque in a steady state and the total value of theconsumption current becomes minimal. The STM set current in the steadystate is, for example, 1.8 A. The DCBL drive current in the steady stateis, for example, 0.05 A.

Second Embodiment

A second embodiment of the present invention will be described. Theembodiment is different from the first embodiment as below. That is, inthis embodiment, a test mode is performed in a case in which a specialsheet not corresponding to any load condition of the table in which theSTM set current and the DCBL drive current are registered for each loadcondition is conveyed and an image is formed thereon. Since the otherpoints of this embodiment are the same as those of the first embodiment,a repetitive description will be omitted or simplified.

FIG. 13 is a flowchart illustrating an operation of the image formingapparatus. The flowchart can be performed according to a program by thecontroller 110 of the image forming apparatus 100.

The controller 110 determines whether the sheet for forming the imagethereon is the special sheet on the basis of the print job (S201).

When the sheet to form the image thereon is not the special sheet (S201:NO), the controller 110 sets the STM set current and the DCBL drivecurrent on the basis of the table (S209) and forms the image on theconveyed sheet (S208).

When the sheet to form the image thereon is the special sheet (S201:YES), the controller 110 performs the test mode by steps S202 to S207.

The controller 110 calculates the required torque (S202). The requiredtorque can be calculated on the basis of the thickness and the stiffnessof the sheet. The material of the roller or the roller diameter of theregistration roller 171 to which the power is transmitted from thestepping motor 210 and the DC brushless motor 220 through the driveshaft can be considered in the calculation of the required torque. Therequired torque may be calculated by referring to a torque tableregistered for each of the thickness and the stiffness of the sheet.

The controller 110 sets the STM set current sufficient for the requiredtorque (S203).

The controller 110 measures the total value of the consumption currentby measuring the STM drive current at the time of conveying the sheet inthe steady state and calculating the DCBL drive current (S204).

The controller 110 determines whether the total value of the consumptioncurrent is smaller than the previous measurement value (S205).

When the total value of the consumption current is smaller than theprevious measurement value (S205: YES), the controller 110 decreases theSTM set current to decrease the STM drive current and to increase theDCBL drive current (S206). The controller 110 repeats step S204 to stepS206 until the total value of the consumption current becomes equal toor larger than the previous measurement value.

When the total value of the consumption current is not smaller than theprevious measurement value (S205: NO), the controller 110 sets the STMset current and the DCBL drive current set in the previous measurementas the STM set current and the DCBL drive current in the steady state(S207) and forms the image on the conveyed sheet (S208).

The embodiment according to the present invention has the followingeffects.

When the same drive shaft is driven by different torques of two motors,it is possible to suppress the consumption current of the motor in thesteady state by optimizing each motor drive current setting value.

Further, each motor drive current setting value is optimized so that thetotal value of the consumption current becomes minimal on the basis ofthe load condition. Accordingly, it is possible to improve the motorconsumption current suppressing effect in the steady state.

Further, the load condition is set to at least any one of the sheettypes and the conveying speed of the sheet conveyed by the roller towhich power is transmitted from two motors through the drive shaft.Accordingly, it is possible to more simply and effectively suppress themotor consumption current in the steady state.

Further, the first motor which is one of the two motors is set as thestepping motor and the second motor having the torque smaller than thatof the first motor is set as the DC brushless motor. Accordingly, it ispossible to more simply obtain the drive current setting value optimizedto each motor.

Further, each drive current setting value in which the total value ofthe consumption current which changes by decreasing the drive currentsetting value of the first motor from a current value for generating therequired torque and increasing the drive current setting value of thesecond motor becomes minimal is set at the time of setting each motordrive current setting value in which the total value of the consumptioncurrent becomes minimal. Accordingly, it is possible to efficientlyobtain the drive current setting value optimized to each motor.

Further, the drive current setting value of the first motor in which thetotal value of the consumption current becomes minimal is calculated asthe first setting value from the relational expression of the drivecurrent setting value of the first motor and the total value of theconsumption current corrected by the first load parameter depending onthe load condition. The second motor drive current setting valueobtained by applying the first setting value to the relationalexpression of the drive current setting value of the second motor andthe first setting value corrected by the second load parameter dependingon the load condition is calculated as the second setting value. Then,each motor drive current is set on the basis of the first setting valueand the second setting value. Accordingly, it is possible to reduce astorage capacity necessary for calculating the drive current settingvalue optimized to each motor.

Further, each motor drive current setting value is set by referring tothe table that each motor drive current setting value in which the totalvalue of the consumption power becomes minimal is registered for eachload condition. Accordingly, it is possible to shorten a calculationtime for calculating the drive current setting value optimized to eachmotor.

Further, the second motor drive current is linearly increased inaccordance with an increase in rotation speed of the first motor at thetime of increasing the conveying speed to the setting speed in thesteady state. Accordingly, since the torque at the low conveying speedcan be ensured only by the first motor, it is possible to reduceconsumption power and to prevent from stepping out by preventing anexcessive torque from being supplied by the second motor in anacceleration state.

Further, the load condition includes the nip pressure at the nip portionformed by the roller and the other roller. Accordingly, it is possibleto suppress the motor consumption current according to the actualmachine condition.

Further, the load condition includes the temperature. Accordingly, it ispossible to more suppress the motor consumption current according to theactual machine condition.

Further, the load condition includes the load on the roller due to thepulling of the sheet caused by the conveying speed difference at theupstream and downstream of the roller. Accordingly, it is possible tofurther suppress the motor consumption current according to the actualmachine condition.

Further, the test mode is performed when the sheet type of the conveyedsheet is the special sheet not corresponding to any load condition ofthe table that each motor drive current setting value in which the totalvalue of the consumption power becomes minimal is registered for eachload condition. Accordingly, it is possible to suppress the motorconsumption current by coping with the special sheet not registered inadvance.

The conveying driving device, the conveying driving device controlmethod and program, the motor drive current setting table generatingmethod and program, the image forming apparatus, and the image formingapparatus control method and program of the present invention are notlimited to the above-described embodiment.

For example, the conveying driving device of the present invention canbe applied as the conveying driving device of the loop roller and theother rollers.

Further, in the embodiment, a part or all of the processes performed bythe program may be performed by hardware such as a circuit.

Although embodiments of the present invention have been described andillustrated in detail, the disclosed embodiments are made for purpose ofillustration and example only and not limitation. The scope of thepresent invention should be interpreted by terms of the appended claims.

1. A conveying driving device comprising: a first motor which transmitspower to a drive shaft of a roller; a second motor which transmits powerto said drive shaft along with said first motor at a torque smaller thanthat of said first motor; and a hardware processor which sets each ofdrive current setting values of said first motor and said second motorso that a total value of a consumption current of said first motor andsaid second motor becomes minimal in a steady state in which said rollerrotates at a constant setting speed.
 2. The conveying driving deviceaccording to claim 1, wherein said hardware processor sets each of thedrive current setting values of said first motor and said second motorin the steady state so that the total value of the consumption currentof said first motor and said second motor becomes minimal in said steadystate on the basis of a load condition on said roller.
 3. The conveyingdriving device according to claim 2, wherein said load condition is atleast one of a sheet type and a conveying speed of a recording mediumconveyed by said roller.
 4. The conveying driving device according toclaim 1, wherein said first motor is a stepping motor and said secondmotor is a DC brushless motor.
 5. The conveying driving device accordingto claim 1, wherein said hardware processor measures the total value ofsaid consumption current which changes by decreasing the drive currentsetting value of said first motor in said steady state from a currentvalue for generating a torque equal to or larger than a torque fortransmitting required power to said drive shaft in said steady state andincreasing the drive current setting value of said second motor and setseach of the drive current setting values of said first motor and saidsecond motor when the total value of said measured consumption currentbecomes minimal as the drive current setting values of said first motorand said second motor in the steady state.
 6. The conveying drivingdevice according to claim 2, wherein said hardware processor calculatesthe drive current setting value of said first motor in which the totalvalue of said consumption current in said steady state becomes minimalas a first setting value from a relational expression of the drivecurrent setting value of said first motor in said steady state and thetotal value of said consumption current in said steady state correctedby a first load parameter depending on said load condition, calculatesthe drive current setting value of said second motor obtained byapplying said calculated first setting value to a relational expressionof the drive current setting value of said second motor in said steadystate and said first setting value corrected by a second load parameterdepending on said load condition as a second setting value, and setseach of the drive current setting values of said first motor and saidsecond motor in said steady state on the basis of said first settingvalue and said second setting value.
 7. The conveying driving deviceaccording to claim 2, wherein said hardware processor sets each of thedrive current setting values of said first motor and said second motorin said steady state for each said load condition by referring to atable that the drive current setting values of said first motor and saidsecond motor when the total value of said consumption current in saidsteady state becomes minimal are registered for each said loadcondition.
 8. The conveying driving device according to claim 1, whereinsaid hardware processor linearly increases the drive current settingvalue of said second motor in accordance with an increase in rotationspeed of said first motor at the time of increasing the rotation speedof said roller to said setting speed in said steady state.
 9. Theconveying driving device according to claim 2, wherein said loadcondition includes a nip pressure at a nip portion formed by said rollerand the other roller.
 10. The conveying driving device according toclaim 2, wherein said load condition includes a temperature.
 11. Theconveying driving device according to claim 2, wherein said loadcondition includes a load on said roller due to the pulling of therecording medium caused by a conveying speed difference at the upstreamand downstream of said roller.
 12. The conveying driving deviceaccording to claim 7, wherein said hardware processor performs a testmode when a sheet type of said recording medium conveyed by said rolleris a special sheet not corresponding to any said load condition of saidtable that the drive current setting values of said first motor and saidsecond motor are registered for each said load condition, and wherein insaid test mode, the hardware processor calculates a torque fortransmitting required power to said drive shaft in said steady state onthe basis of a thickness and a stiffness of said recording medium,measures a total value of a drive current of said first motor and saidsecond motor in said steady state at the time of conveying saidrecording medium by said roller after setting the drive current settingvalue of said first motor to a value for generating a torque equal to orlarger than at least the calculated torque, and determines the drivecurrent setting values of said first motor and said second motor whenthe total value of the consumption current of said first motor and saidsecond motor becomes minimal by repeatedly decreasing the drive currentsetting value of said first motor and increasing the drive currentsetting value of said second motor until the measurement value becomesequal to or larger than the previously measured total value of the drivecurrent of said first motor and said second motor when the previouslymeasured value is smaller than the total value of the drive current ofsaid first motor and said second motor.
 13. A control method for aconveying driving device comprises a first motor which transmits powerto a drive shaft of a roller and a second motor which transmits power tosaid drive shaft along with said first motor at a torque smaller thanthat of said first motor, the control method comprising: setting each ofdrive current setting values of said first motor and said second motorso that a total value of a consumption current of said first motor andsaid second motor becomes minimal in a steady state in which said rolleris rotated at a constant setting speed.
 14. A non-transitorycomputer-readable storage medium storing a control program for aconveying driving device comprises a first motor which transmits powerto a drive shaft of a roller and a second motor which transmits power tosaid drive shaft along with said first motor at a torque smaller thanthat of said first motor, the control program causing a computer toperform: setting each of drive current setting values of said firstmotor and said second motor so that a total value of a consumptioncurrent of said first motor and said second motor becomes minimal in asteady state in which said roller is rotated at a constant settingspeed.
 15. A method of generating a table used to set drive currentsetting values of a first motor and a second motor in a steady state inwhich a roller rotates at a constant setting speed in a conveyingdriving device, the conveying driving device comprises said first motorwhich transmits power to a drive shaft of said roller and said secondmotor which transmits power to said drive shaft along with said firstmotor at a torque smaller than that of said first motor, the method ofgenerating the table comprising: measuring a total value of aconsumption current of said first motor and said second motor whichchanges by decreasing the drive current setting value of said firstmotor in said steady state from a current value for generating a torqueequal to or larger than a torque for transmitting required power to saiddrive shaft in said steady state and increasing the drive currentsetting value of said second motor; determining the drive currentsetting values of said first motor and said second motor when the totalvalue of said measured consumption current becomes minimal; andgenerating said table by registering the determined drive currentsetting values of said first motor and said second motor.
 16. The methodof generating the motor drive current setting table according to claim15, wherein in the step of measuring, the total value of saidconsumption current of said first motor and said second motor ismeasured for each load condition on said roller, wherein in the step ofdetermining, the drive current setting values of said first motor andsaid second motor when the total value of said measured consumptioncurrent becomes minimal are determined for each said load condition, andwherein in the step of generating, the drive current setting values ofsaid first motor and said second motor determined for each said loadcondition are registered to generate said table.
 17. A non-transitorycomputer-readable storage medium storing a program for generating atable used to set drive current setting values of a first motor and asecond motor in a steady state in which a roller rotates at a constantsetting speed in a conveying driving device, the conveying drivingdevice comprises said first motor which transmits power to a drive shaftof said roller and said second motor which transmits power to said driveshaft along with said first motor at a torque smaller than that of saidfirst motor, the program causing a computer to perform the method ofclaim
 15. 18. The non-transitory computer-readable storage mediumstoring the program for generating the motor drive current setting tableaccording to claim 17, wherein in the step of measuring, the total valueof said consumption current of said first motor and said second motor ismeasured for each load condition of said roller, wherein in the step ofdetermining, the drive current setting values of said first motor andsaid second motor when the total value of said measured consumptioncurrent becomes minimal are determined for each said load condition, andwherein in the step of generating, the drive current setting values ofsaid first motor and said second motor determined for each said loadcondition are registered to generate said table.
 19. An image formingapparatus comprising: a first motor which transmits power to a driveshaft of a roller conveying a recording medium; a second motor whichtransmits power to said drive shaft along with said first motor at atorque smaller than that of said first motor; a hardware processor whichsets each of drive current setting values of said first motor and saidsecond motor so that a total value of a consumption current of saidfirst motor and said second motor becomes minimal in a steady state inwhich said roller rotates at a constant setting speed; and an imageformer which forms an image on said conveyed recording medium.
 20. Theimage forming apparatus according to claim 19, further comprising: astorage which stores a table that the drive current setting values ofsaid first motor and said second motor when the total value of saidconsumption current becomes minimal in said steady state are determinedfor each load condition on said roller, wherein said hardware processorsets each of the drive current setting values of said first motor andsaid second motor in said steady state for each said load condition byreferring to said table.
 21. A control method for an image formingapparatus comprises a first motor which transmits power to a drive shaftof a roller conveying a recording medium, a second motor which transmitspower to said drive shaft along with said first motor at a torquesmaller than that of said first motor, and an image former which formsan image on said conveyed recording medium, the control method for theimage forming apparatus comprising: specifying a load condition on saidroller on the basis of a print job; determining drive current settingvalues of said first motor and said second motor corresponding to saidspecified load condition by referring to a table that the drive currentsetting values of said first motor and said second motor when a totalvalue of a consumption current of said first motor and said second motorin a steady state in which said roller rotates at a constant settingspeed becomes minimal are determined for each said load condition; andsetting the drive current setting values of said first motor and saidsecond motor in said steady state on the basis of the determined drivecurrent setting values of said first motor and said second motor.
 22. Anon-transitory computer-readable storage medium storing a controlprogram for an image forming apparatus comprises a first motor whichtransmits power to a drive shaft of a roller conveying a recordingmedium, a second motor which transmits power to said drive shaft alongwith said first motor at a torque smaller than that of said first motor,and an image former which forms an image on said conveyed recordingmedium, the control program causing a computer to perform the method ofclaim 21.